Due to higher and higher degrees of integration of semiconductor circuits and the application of photolithography technology to form such semiconductor circuits, it is necessary to ensure a high degree of evenness or flatness of the surface of the semiconductor wafer onto which the circuits are to be applied. To even or flatten a surface of a semiconductor wafer, typically, a polisher is employed which includes a plurality of rotatable wafer carriers and a turntable with a polishing member such as a polishing pad, a grinding stone or a whet stone. Each of the rotatable carriers supports a wafer in such a manner that the wafer is kept in contact with the polishing surface of the turntable. The turntable is being rotated around a center axis passing through the center of and normal to the polishing surface of the turntable while abrasive slurry is supplied between the polishing surface and the surface of the wafer to be polished.
In such a polisher, an endpoint of the polishing is usually determined by timing the polishing operation on the basis of a polishing rate. The polishing rate is usually determined by conducting a test polishing in advance of an actual polishing. However, since the polishing rate can vary depending on changes in the polishing conditions, such as, the polishing surface, the pressure between a wafer and the polishing surface and so on, it is difficult to precisely determine the endpoint of the polishing only on the basis of trial timing. Another method for determining the endpoint of a polishing operation involves detecting a change in the torque of a motor rotating the turntable or wafer carrier by measuring an electric current supplied to the motor rotating the turntable or wafer carrier. A change in torque being effected when a certain amount of a dielectric material layer is removed, exposing the top surfaces of the semiconductor circuits which underlay the dielectric material layer. However, the resulting change in rotational torque is small and thus, it is difficult to accurately detect a change in electric current.
Another method for determining the endpoint of a polishing operation involves detecting a change in a vibration of a rotating wafer or wafer carrier which also occurs when the top surfaces of the semiconductor circuits are exposed. However, since the vibration is conventionally detected by an electrical vibration detector mounted on the rotational wafer carrier assembly and the electrical signal generated by the detector is received by a controller provided on a stationary part of the polisher, an electrical connector consisting of a stationary contact element and a rotational contact element rotationally engaged with the stationary element, are required to be provided between the stationary part and the rotational wafer carrier assembly. However, the noise generated in such a connector influences the vibration detection system. Further, such an electrical connector requires periodic maintenance. A similar connector is also needed to supply electric power to the vibration detection system.